7a lies on the cortical surface, between the IPS and the STS, just dorsal (external) to LIP. It occupies the more caudal/medial aspect of this region, with 7b more rostral/lateral. Pandya and Selzer call it PG (and maybe PGF).
Moderate sized
contra-lateral visual receptive fields, 10-20deg.
There is a good deal of saccadic activity, attentional modulations,
planning, etc. LIP shows
memory or delay activity for pending saccades (and other spatially oriented
behaviors). LIP “remaps” activity after an intervening saccade.
Topography: There seems to be a very local topography, i.e. as you move along tangential to surface, saccade preferred directions (PDs) change smoothly. However there is only the roughest of global topographies: D-V = Central – Peripheral, A-P = Lower – Upper (Blatt et al 1990). Many repeats, breaks in topography. (Note this is similar to V3, V4; Blatt et al 1990).
7a is thought to be the most important area for spatial perception. Hemi-neglect is apparently produced from lesions of 7a alone.
7a vs LIP:
Both areas (as well as DP) have saccadic responses, but 7a has fewer such cells, and the activity is post-saccadic. All three areas show eye-position effects.
7a vs 7b:
Responses in 7a are primarily visual and motor related, as compared with 7b, which is largely somatosensory. This distinction is (roughly) true of cortical connectivity as well.
7a is connected to (all due to AAES):
Visual areas: PO, TF, IT, TEo
IPL/STS: MST, STP, FST,
Frontal Cortex: 8a (FEF),
46, 45, 11(?), SEF
Cingualte: LC, LA(?)
AAES: “Area 7a appears to be very different from the other visual areas in the IPL in that is is the only area that connects to some of the highest centers of the brain including the cingulated gyrus, large areas of the parahippocampal gyrus, the presubiculum, area PGm, and the rostral superior temporal sulucus, including the the inferotemporal cortex. This last … is particularly important… direct connection between the area thought to be most crucial for object perception and the area thought to be most crucial for spatial perception.”
A hierarchy from AAES…. Note, they say, Traditionally, feedforward connections derive from supra-granular layers (I-III) and terminate in middle layers (III-IV). Feedback from supra- and infra-granular layers terminates in I and VI. They found that almost all projections derived from III, V, and VI, and so used terminations to determine the hierarchy.